1. Field of the Invention
The present invention relates to a controllable integrated optical component comprising a substrate having electro-optical properties into which at least one optical waveguide is introduced and wherein metallizations in the form of a plurality of electrodes which are chargeable with electrical voltages are applied on or next to at least one optical waveguide.
2. Description of the Prior Art
Controllable integrated optical components such as, for example, directional couplers or Mach-Zehnder interferometers are employed as switches or modulators. An electrical field is used for the modulation of light given electro-optical components. In the simplest arrangement, the phase modulator, the refractive index is altered with the assistance of the electrical field and the propagation constant .beta. and, therefore, the phase relation of the light are modulated as a result thereof. The intensity of the light can be modulated in various ways with corresponding electrode and waveguide arrangements. An electrical field can, for example, be employed to control a reflecting layer such that light is partially or completely reflected. Further, the refractive index of a waveguide can be lowered to such a degree with an electrical field that the intensity of the guided light beam is partially or entirely coupled over into substrate modes. The controllable directional coupler which comprises coupled waveguides is one of the most important electro-optical components. The intensity modulation or, respectively, transfer of the light to one of the output waveguides is thereby based on the electrical detuning of the coupled waveguides. The detuning occurs by way of an opposing variation of the refractive index in the coupled waveguides. An improvement of the modulation depth or, respectively, of the crosstalk attenuation is possible with a modified directional coupler in the manner of the alternating delta-beta principle, as has been disclosed in the article of H. Kogelnik and R. V. Schmidt in the periodical IEEE J. Quantum Electronics, Vol. 1976, QE-12, pp. 396-401. The electrodes of the directional coupler are thereby divdided into individual sections and are driven with alternating modulation voltage. Given the intensity modulator according to the Mach-Zehnder principle, the incoming, guided light energy is uniformly divided onto two waveguides. The resulting waves in these two waveguides are then electro-optically phase modulated in different manners. Intensity-modulated light arises at the output of the Mach-Zehnder interferometer due to interference after the combination of these two waves.
The German Letters Patent No. 32 18 626, fully incorporated herein by this reference, discloses a controllable integrated optical component in which metallizations in the form of a plurality of electrodes are applied on or next to the optical waveguide, the electrodes being chargeable with electric voltages, whereby a coplanar microwave line is disposed next to the optical waveguides, and whereby respectively one electrode is connected to a respective strip of the microwave line via a line which is as short as possible. Given such a controllable integrated optical component, the advantages of a traveling wave line, namely a fundamentally attainable, high modulation bandwidth, are combined with the advantages of concentrated electrode sections, namely a flexible selection of the voltage polarity at the electrodes. In that the radio frequency line in this known integrated optical component is no longer bound to the dimensions of the optical waveguides, this radio frequency line can have rather large cross-sectional dimensions. A very low series resistance of the radio frequency line derives in this manner. An alternating voltage polarity can be supplied to the electrodes and, therefore, an alternating electrical field can be supplied to the optical waveguides without difficulty in that the electrode sections can be connected to the radio frequency line in this known integrated optical component by way of short bond connection. In this manner, for example, the advantageous alternating delta-beta principles can be connected with the advantages of a broadband traveling wave line. In that the radio frequency line is disposed next to the optical waveguides, given this known integrated optical component, the radio frequency line can be applied without difficulty to a different dielectric material with which the optical substrate can be laterally coated or which is separately disposed next to the optical waveguides. When the radio frequency line is applied, for example, to ceramic or, even better, to silica glass and the electrodes are located on lithium niobate, such a phase velocity can be created for the controlling radio frequency wave in this manner at the optical wave in the optical waveguides in lithium niobate and the controlling wave on the radio frequency line approach one another with respect to their phase velocities. The manufacture of the bonded connections between the individual electrodes and the respective strip of the microwave line is involved, given this known integrated optical component. With such a known integrated optical component, the long bonded connections have relatively high inductances, the frequency response in this known integrated optical component being deteriorated as a result thereof. Moreover, these bonded connections are of different lengths, this again resulting in inductances of different magnitudes. These differing inductances, however, hardly allow a reproducible microwave mode of such a known integrated optical component.